1. Field of the Invention
The present invention relates to a method for thinning a substrate such as a semiconductor wafer, and a method for manufacturing a circuit device.
2. Description of the Prior Art
There is a need to make IC cards or cell phones thinner, smaller, and lighter. In order to satisfy this need, a semiconductor chip to be incorporated therein must be thin. Although the thickness of a wafer which forms a semiconductor chip is 125-150 μm at present, it is expected that the thickness of a semiconductor wafer must be 25-50 μm for a next generation chip.
An example of a conventional method for thinning a semiconductor wafer has been disclosed in Document 1. According to this method, a supporting plate made of a rigid material such as glass, ceramic, or metal is attached to a surface of a semiconductor wafer on which a circuit device has been formed, so that the supporting plate and the semiconductor wafer are united. The supporting plate in this united state is fixed to an attracting head, and the rear surface of the semiconductor wafer is ground by a grinder to thin the wafer.    [Document 1] Japanese Patent Application Publication No. 2005-150434
In the method disclosed in Document 1, the supporting plate needs to be stripped from the thinned semiconductor wafer before the subsequent dicing step. However, since the supporting plate and the semiconductor wader are bonded to each other with no gap by using an adhesive, it is difficult to strip.
Thus, the present inventors have proposed a supporting plate provided with a plurality of penetrating holes through which solvent can flow to the adhesive.
In order to thin (grind) a substrate by using this supporting plate, after a layered structure is formed by attaching the supporting plate to a surface of a semiconductor wafer W (on which a circuit device has been formed), the supporting plate side of the layered structure is mounted and fixed onto an attracting head as shown in FIG. 6. The other surface of the semiconductor wafer (the reverse or opposite surface of the surface on which a circuit device has been formed) is ground by a grinder in this state.
However, in this method for thinning a substrate, since attraction (vacuum attraction) is performed throughout grinding, the pressure inside the penetrating holes is reduced by negative pressure at the time of vacuum attraction. Consequently, there are cases where the pattern of the penetrating holes is transferred to the surface of the thinned semiconductor wafer W on which a circuit device has been formed through the adhesive layer.
There are also cases where the semiconductor wafer W is drawn to the attracting head side through the supporting plate and the adhesive layer by negative pressure at the time of vacuum attraction when the other surface of the semiconductor wafer W is ground by a grinder.
In this instance, since the wafer W is spaced apart from the grinder, some problems might arise such as non-uniform grinding of the other surface of the semiconductor wafer or an increase in the surface roughness. If another circuit device is formed in the other surface of the semiconductor wafer W, these problems might affect the properties of such a circuit device.
In order to solve the above-mentioned drawbacks, an object of the present invention is to provide a method for thinning a substrate and a method for manufacturing a circuit device which make it possible to prevent the pattern of penetrating holes from being transferred to the substrate and prevent problems such as non-uniform grinding of the surface of the substrate from occurring.